MM ----- I reckon the general rule-of-thumb that people pass around ---- about repotting when new roots are appearing .... is just a rule-of-thumb. I repot any catt and pretty much any of my tropical orchids at any time, and nothing bad will happen to them. Some people mention bifoliate catts - in particular bifoliate species catts - really need to be repotted when roots are sprouting etc. I don't think that's correct either. I'll repot any regular sort of catt --- species or hybrid - bifoliate or unifoliate. Any time.repotting them at the correct time, when new roots are appearing from the new shoot.
It is true OP. Very true. It probably also depends on whether the roots of a catt are adapted to lower oxygen level environments or wet environments (or not). But in general ----- for regular catt roots, I like the suggestions about air-flow around the roots ----- through the media etc. A shallow pot and airy media will definitely help in that way.I wonder if the deep plastic trays diminish airflow around the pot and root area, facilitating rot. I would try a shallower vessel. Catts grow on trees with lots of air around the roots. An idea to contemplate.
One thing I do in deep 7” or all 8” - 10” (my largest) pot, is to put a 2” net pot upside down in the center bottom (secured with twist ties) and use a soldering iron to put holes in the center bottom of the pot under the net pot for air to enter. Keith Davis recommended the net pot idea.It is true OP. Very true. It probably also depends on whether the roots of a catt are adapted to lower oxygen level environments or wet environments (or not). But in general ----- for regular catt roots, I like the suggestions about air-flow around the roots ----- through the media etc. A shallow pot and airy media will definitely help in that way.
One method I use that works for wide pots (or wide-enough) pots - that can also be deep too ---- is the method of dumping most of the water toward the outskirts of a suitably large size pot. If the bulk of media in the pot (such as the central region - and down in the deep dark depths) is prevented from becoming a wet slush/slurry/sludgy saturated mix --- especially around the bulk of the roots ----- then that will help catts (and other orchids) out ----- by not getting into long-time wet roots condition.
When watering the outskirts of the pot, while having the inner regions dryer (much less wet) ..... it might be possible that (using a pot having good size drainage holes at the bottom) the roots can have nice humid conditions to grow well ----- with a wet/dry gradient inside the pot.
If an orchid grower finds that - when they unpot a catt and see a big mass of soft mushy gray/olive/dark water logged roots ...... then the pot may just not be large/wide enough, or the media not quite airy enough, or the watering strategy/plan isn't suitable. Also knowing that 'very cold plus very wet' isn't good too for roots.
There can be exceptions. For example ----- if an orchid just-so happens to have its roots grow out (naturally reach out) into a very wet medium, then its roots may well somehow 'adapt' to that particular wet or low oxygen environment. So some people expecting to pull out a mass of mushy dead roots can sometimes be 'surprised' when they see a mass of nice green/white wet roots. It can mean the roots 'adapted' to the environment. But roots apparently (we've been told) can handle low-oxygen watery environments up to a point or a limit. So that just means growers be 'warned' about what could happen ..... such as a mass of nice adapted green/white roots could take a dive in health if something doesn't go well - such as bacterial activity/rotting starts up if portions of roots get into trouble due to not enough O2 ----- then one thing leads to another.
So - keeping control of the conditions within the pot and in/around the roots is very important (this is well-known) ---- aside from the conditions in and around the leaves/stem (temperature and temperature changes and rates of temperature changes, air-movement etc).